Solid axle suspension can suffer from binding or memory steer of the steering joint as a result of misalignment of the supporting rotational joints. The service life of the rotational joints can be reduced due to the increased wear caused by misalignment.
A solid axle suspension, as opposed to independent suspension, is commonly used in larger vehicles such as trucks, vans and sport utility vehicles. The solid axle requires the wheel hub to rotate about an axis to provide steering. Two rotational joints connect a center axle along the rotational axis to the wheel yoke that houses the wheel hub.
The pair of rotational joints that connect the center axle and yoke are usually found in two configurations, namely a pair of conventional ball joints and alternatively a single ball joint combined with a rotating joint that only rotates and can move axially (translate along the rotational axis). Axial motion or translation is required for proper installation to allow movement of the rotational stud when assembling the yoke and center axle together.
The axis of rotation of the stud, in the rotational joint, also determines the axis of rotation of the yoke-center axle assembly. Accordingly the pair of joints must align on the same rotational axis. To allow the yoke to rotate on the center axle, the spherical center of the ball joint must lie on the rotational axis of the rotational joint.
FIG. 1 is an exploded isometric view of a prior art automotive solid axle with a suspension center axle 1, and yoke 2 housing the wheel hub 3. The center axle 1 and yoke 2 are connected at and rotate about a rotational axis 4 on two rotatable joints 5, 6. FIG. 2 is a schematic sectional view through the prior art center axle 1 and yoke 2 along the axis of rotation 4, showing a misalignment of the spherical center 7 of the upper ball joint 5 and the rotation axis 4 of the lower rotatable joint 6. FIG. 2 shows the misalignment as dimension “x”. The misalignment can cause an issue commonly referred to as memory steer.
When the ball joint 5 and the rotational axis 4 are misaligned, the rotating joint 6 experiences forces and stresses which lead to premature failure. To compensate for the misalignment, original equipment manufacturers often use malleable materials such as plastic for bearings to permit a degree of deformation under stress and allow the pair of joints to self-align. The deformation allows the joints to align and mitigates any significant memory steer. However deformation of plastic bearings also shortens the service life of the rotating joint.
Further use of plastic bearings may permit self-alignment under stress, and be less expensive but plastic bearings have a shorter service life than metal bearings in general even without misalignment, and plastic bearings can be easily damaged by high loads, heat and impact.
Features that distinguish the present invention from the background art will be apparent from review of the disclosure, drawings and description of the invention presented below.